1. Field of the Invention
The present invention relates to an image pickup apparatus, a method of controlling the same, and a storage medium, and more particularly to an image pickup apparatus that picks up an object using a rolling shutter method, a method of controlling the same, and a storage medium.
2. Description of the Related Art
Conventionally, as an exposure system used in an image pickup operation, there have been known a global shutter method and a rolling shutter method. In an image pickup apparatus using the global shutter method, which is represented by an image pickup apparatus including a CCD sensor, the exposure time period and the exposure start time are substantially the same between pixels of one frame image.
On the other hand, in an image pickup apparatus using the rolling shutter method, represented by an image pickup apparatus including a CMOS sensor, although the exposure time period is the same between pixels in one frame image, the exposure start time is different for each scan line.
Therefore, in the image pickup apparatus using the CMOS sensor, an image distortion caused by the rolling shutter (hereinafter referred to as the “rolling-caused distortion”) occurs.
Further, electronic image stabilization has been proposed as processing for reducing camera-shake blur in an image picked up by the image pickup apparatus by adjusting a clipping position of image data temporality stored in a memory.
The electronic image stabilization is processing for reducing camera-shake blur in an image picked up by the image pickup apparatus by calculating an amount of movement of the image pickup apparatus e.g. from a motion vector detected using a gyroscope and adjusting a clipping position of image data from the memory according to the calculated movement amount.
In such a technical background, there has been disclosed a technique that collectively performs correction of camera-shake blur and correction of image distortion due to a rolling shutter in an image picked up by an image pickup apparatus (see e.g. Japanese Patent Laid-Open Publication No. 2006-186885).
However, in the image pickup apparatus disclosed in Japanese Patent Laid-Open Publication No. 2006-186885, there is no description of processing to be performed when an area to be referred to for correcting rolling-caused distortion occurring in the image picked up by the image pickup operation using the rolling shutter method is outside the range of an area on a memory from which image data is to be clipped. In the cause of such processing, the area to be referred to is sometimes outside an area in which image data has been stored. In an area outside the range of the area where image data has been stored, data irrelevant to images, i.e. invalid data as image data (so-called junk data) exists. Therefore, if distortion correction processing is performed without adjusting the area to be referred to, data including invalid data is sometimes output.